Signaling system



July 4; 1944.

M. l. HULL S IGNALING SYSTEM Original Filed July 18, 1938 4 Sheets-Sheet 1 REA.

.rlll II" L 1 MAUIPY HULL INVENTOR ATTORNEY y 1944- M. HULL 2,352,634

SIGNALING SYSTEM ori inal Filed July 18, 1938 4 Sheets-Sheet 2 Fig. 4-.

v Mum HuLz.

INVENTOR I ATTORNEY July 4,1944. M. l. HULL 2,352,634

SIGNALING SYSTEM Original Filed July l8, 1958 4 Sheets-Sheet 3 MA urw HULL I ATTORNEY 4 Sheets-Sheet 4 M. l. HULL SIGNALING SYSTEM Original Filed July 18, 1938 MA u I? Y I /ULL y INVENTOR ATTORNEY July 4, 1944.

REA.

Patented July 4, 1944 SIGNALING SYSTEM Maury L'Hull, Memphis, Tenn.

Original application July 18, 1938,, still No. 219,785. Divided and this application November-17, 1941,;Serial No.419,471- Y I H H 'l iClainis; (015250-99 (Grautedunder,.1thc act of March 3, ate, as f} 1 ,gamended April 30, 1928; 370 Q. ,G. 757)..

This-application is-a division of myapplication Serial Number 219,785, filed July 18, 1938 (Patent No. 2,262,764," granted November 18, 1941). I v

This invention relates to signaling systems and more particularly to systems for transmitting and receiving-a plurality of'signals simultaneously.

- An object of the invention is to'provide a system in which a pluralityor signals maybe transmitted andreceived on a single carrier wave.- With this object in'view my invention contem plates anarrangement in which alternate cycles or groups of cycles of a -'carrier frequency are modulated by signals from two separate sources, therate of alternation being above audibility.

The invention may beajdapted't'o the transmission and reception" of more than two messages simultaneously. j I Further objects of my invention are to provide .in a wave transmission systema novel means whereby a voltage bearing s p-harmonic relationship to a carrier frequencyjs used to insure that alternate cycles or groups of cycles of the carrier wave are modulated by separate intelligence'and insa receiveizto provide novel means whereby a voltage bearing a sub-harmonic relationship to the received carrieris used to insure that-the carrier modulated at the transmitter in thefa'shion described'above :is :so broken up in the receiver in synchronism with'the incoming signals that the two or more intelligences are'properlysepfa-' rated-a.nd'received.- h

Other and further objects of the invention will be apparent from the following specification when read inco'nnection with the accompanying drawings in which: 7 v

Figure 1 is a circuitdiagram of a preferred form oftransmitting circuit and arrangement for accomplishing the purpose'of the invention. Figures 2 and '3 are curves illustrating the operation of the transmitting system shown in Figure 1. c i l Figure 4is a circuit diagram showing modifications of the transmitting system shown Fig,-

ure 1.

Figure 5 is a circuit diagram showing how. the transmitter Figure 1 may be modified for the transmission of four intelligences simultaneously.

v, Figure 6 is a curve illustrating the operation of the transmitting system shown in Figure 5.

v Figure 7 is .a circuit diagram of a preferred form of receiving apparatuswhichmaybe ,em- .ployed. I

, Figure Sis a curve illustrating the operation of the receiving'systemfihownin Figure 7. I

In Figure 1 the rectangle designated 8.50. is

a source of radio frequency oscillations of 'any convenient. desired, freq en y-j. t i pr f blya piezo electric crystal controlled, vacuum tube oscillator but it may, takeany of several known forms. The output from thesourceiofuo'scillations S. Q. is connected to, the input circuitof a radio frequency amplifiershown as a rectangle designated R. F. A. The radio frequency amplifier. RF. A. isapreferably;.of.the.vacuumtube typewith-a resonant plate circuit load, but it may be any oneiof. many well known gamplifier circuits. The' output ofytheradio; frequency, amplifier RF. A. is.connected :to the. input circuit of a-phase shifter shown asa rectangle vdesignated P. S. The output of-.,the phase shifter P.. S...is;con-

nected-to the'primaryv of: theradio frequency transformer 1-,2. The secondary .2 of theradio frequency transformer 1+2 is .centerxtapped. The end terminalsof the secondary 2 are connected to the control grids of theavacuum tubes 3 and 4 respectively. .'.The center tap connection of the secondary 2 is. connected to ':one terminal of a source of biasing potentialrE-the other terminal of which is connected tothe cathodes of tubes'3 and 4. .A source'of :anodelonplat'e potential is shown at 6,:oneterminalbei'ng connected to the cathodes :of the tubes .3. and-I while the other :terminal'fis connected to the anodes of tubes? and 4 via the resistances .1: and 8respectively. The-anodesot' tubesii arid-4 areconnected via sourcesof biasing'potentia'l 9 and lflres'pectively to the control -el'ectrode's10fvacuum tubes -l 3 and l l respectively; The midpoint between resistances! and Bis connected to the cathodes oftube's l3 and M by way of the secondary H of a radio frequency'transfonnerl I"--I2.- -The primary ll of-the transformer lI-l2-is ener- 'gized indirectly'by the source of oscillations S. O. in the following mariner, namely:

I The source of oscillations S. 0. has its output connected to the input circuitota frequency multiplier or frequency doubler, the rectangle designated'F. D. :Theloutputof the {frequency multiplier or frequency do'ubler F. "D; is"c'onnected to'the input circuit of a variable"attenuator, the rectangle designated'VA. "Theoutput of the ariable'attenuator V.- A; is co'n'nectelto the primary l l ofthe Y -=tmn'sror1 -ne1- l| fl2. Microphones or other sources-arsenals 'a eshown at al 9 1 and 20 connected 'via amplifiers T and I8 respectively to the primariesio f audio frequency transformers T5 and -16 respectively. One end a ate;

. bias for the grids of these tubes so that with no nected to a source of anode potential 28 by way of the resistance 24. The low potential sides of the anode batteries 21 and 28 are connected together to the cathodes of the tubes I3 and I4.

Radio frequency by-pass condensers "43 and 44 are connected across the secondaries of audio frequency transformers I5 and I6 respectively.

The point in the anode circuit of tube I3 be tween the secondary of transformer I57 and the resistance 23 is connected to one terminal of a coupling condenser 3|, the other terminal of' voltage applied to the transformer I-2 no plate current would flow in the plate circuits of tubes 3 and 4. Then during that part of the cycle of the incoming frequency to transformer I2 which induces a positive potential on' that ter- 7 minal of the secondary 2 which is connected to the grid or control electrode of the tube 3, the

grid of this tube will be made less negative with respect to its filament and current will flow in its plate circuit. At the same instant the other secondary terminal of inductance 2 will be negativeyso that the grid of the tube 4 will be made more-negative, and no current will flow in the plate circuit of tube 4 since this tube is normally biased to cut-off by the voltage of battery :5; andhence the instantaneous increase in negawhich is connected to the control electrode of tube 2|. The point in the anode circuit of tube I4 between thesecondary of transformer I6 and the resistance is connected'to one terminal of a coupling condenser 32, the other terminalof which is connected to the control electrode of-tube 22'. Batteries 29 and '30 supply biasing potentials for the control electrodes of tubes 2| and 22 respectively by way of resistances 25 and -26respectively. a v 1 The plates'or anodesof the tubes 2| and 22 are connected together to one end of the coupling resistor 33, the other end of which is connected to one terminal of a source of "potential or battery the other terminal of. which is connected to the cathodes'of these tubes;

-The anodes of :the tubes 2| and 22 are connected to oneterminalofa coupling condenser 3 1, the-other terminaloflwhich is connected to I the control electrode of the tube '38. Biasing potential is supplied to the control electrode .of the tube 38 from the source of potential 38 by way ofthe resistance 34. The anode of the tube 38 is supplied withpotential from the battery or other source ofipotential-39. by way of primary winding 40. of radio frequency transformer 4 u' 4I. The secondary ':4I- of; the radio frequency transformer is connected to an aerial or other radiating system shown at 42., I

'With tubes I3 and-I4 biased to cut-off by their respective grid bias batteriesso that no current flows in theirirespective anode circuits in the absence of excitation from; transformers I-2 and II"I2, the application of oscillations to the transformer I I,-", I cyclically'change the potential of the grids or-controlelectrodesof tubes l3 and -l4tending to. make the-grids less negative with respect to-their respective cathodes'or filaments (I shall refer to'this hereafter-as the positive, alternationor positive half cycle from secondary I2). Current will flow-:simultaneously in the plate circuits of both tubes I3. 'and I4. I l

On the next half cycle of the radio frequency voltage applied-to; the transformer III2, the grids-of the tubes 13 and I4will-tend to become 7 more negative, and since these tubes are already normally biased to cut-ofiany instantaneous rentattheradiofrequency in the plate circuits 1 ofgtubes I3 and' I I;; These pulsations in this case 'will occur simultaneously vin the output "circuits of tubes I3 and I4. du-ring the;positive'half' of'a cycle .of the voltage introduced in secondary I2. -A sum gn wnthe v ub sl nd .4. arezm; op;-

tive grid voltagedoes not affect the plate circuit of tube 4. During the next half cycle of the incoming voltage introduced in the secondary 2, the potentials across the two terminals are reversed and plate currentfiows in the plate of tube 4 but not in that of tube 3. This type of amplifier is familiarly known as a push-pull amplifier. 7

The currents flowing in the plate circuitsof tubes 3 and 4 cause potential differences across their respective loadresistances :I and 8 which in turn cause instantaneous increases in the negative grid potentials of tubes- I3 and I4, such instantaneous increases in the negative grid potentials of tubes I3 and I4 beingequal to the product of the; instantaneous plate currents in amperes multiplied by the respective values of plate resistances I and}! .in ohms.- The operation above described may be'more readily understood by reference to the curveshown ,in Figure 3 wherein the instantaneous grid voltages on tubes I3 and I4 are shown when both transformers I-'2 and "II-I2 are being excited by voltages of the proper frequency, amplitudes and phasal relationship. r

In Figure 3 the upper section A shows the individual voltages -'operating'in the input circuit' of tube I3, and the lower section B shows the individual voltages operating vin the input section of tube I4. In section A curveI is the steady'negative component'of bias supplied by the battery 9; curve II is'the voltage introduced at I2; curve 111 7 represents the yoltage drop across resistance I occurring on alternate al-. ternations of the input voltageltotransformer V In section B curve I, is the, steady negative biasing'potential" supplied by -they -b attery Ill; curve II is the voltage introduced at I2 and is in the same phase asthat ofcurve .11 of section A; curve III is the voltage drop across resistance 8 occurring on alternate alternations ofthe input voltage to transformer"I+2, and is opposite in phase to the voltage change across resistance I.

Assuming that the frequencymultiplier F. D. doubles the frequency, and assuming that the attenuator V. A and the radio frequency amplifierR. F.A. are relatively adjusted so that'the voltages introduced atthe secondary I2 and those developed by the potential differences across resistances I and 8- for relative amplitudes as shown in Figure 3; and assuming that the phase shifter- PIS. isadjusted so that zero and degrees of'the Iowerincoming frequency from secondary 2 coincides'on the time axis with 270 degrees of the'higher'incoming frequency from the secondary'l2, then it will be seen thatthe positive alternationsor positive half cycles of the incoming radio frequency voltage from the. sec, ondary l2 produceplate currentpulsations in alternate tubes of the two tubes. 13' and 14. If the positive alternation of the first cycle of the in.- coming voltage from the secondary 12 produces a how of current in tube l3,then it does not produce. show of current in tube. M. The corresponding alternation of the next cycle of-voltage from secondary t2 will then produce a flow-of plate current intube H, but not in tube 13. During the. posit ve alternations or positive half cycles of the volt.- age intrd-uced at secondary i2, tube [-3. will have a plate current pulsation during, say, half of,

cycles 1. 3, 5, 7, etc., while tube l4 will have plate. current pulsations during the corresponding half of cycles 2-, 4, 6, 8, etc. This is brought. about by.

the potential difference developed across resist.- ances l and 8 as may be seen by referring to Figure 3.. Curve III as mentioned. before illustrates the instantaneous voltages developed across. re.

Since tubes 3. and 4 are in a push-pull arrange:

ment, their plates draw current alternately and hence alternate voltage. rises shown, by curve III affect alternate tubes of p the group it and I4. CurveII illustrates the voltage introduced at sec ondary l2 which is twice the frequency of that introduced at secondary 2, Due to the circuit arrangement, voltages induced in secondary :2 act simultaneously and similarly on both tubes l3 and [4, so that by referring to Figure 3 it is seen that while the first positive alternation shown in curve 11 would activate both tubes I3 and I4, the corresponding negative voltage rise in curve 111 at the same instant affects only one of the tubes l3 and I4, offsetting the positive voltage of curve II for that part cular tube but not for the other which has aplate currentpulsation due. to its grid potential becoming less negative for an instant. Now' proceeding to the second positive alternation of curve II this time the negative voltage rise shown in curve III, counteracts the effects of. the voltage shown in curve II on a different tube of the group l3-l 4, so that the tube of the group Iii-I4 active before is now idle, while the tube idle before is now active. The process thus continues as long as the excitation ofiradiofrequcncy transformer 2 and .a2 continues with the proper frequency and prope phase and magnitude. 7 These two sets of pulsations in the plate circuits of tubes l3 and I4 are modulated in the plate circuits of their respective tubes by the modulating transformers l and I6, which vary the plate voltages of tubes l3 and I4 and hence vary the magnitude of the redio frequency pulsations in their plate circuits in conformance with the fre-. quency and magnitude of the voice or other signals introduced at microphones l9 and respectively, and amplified by tubes I] and l8 re-. spectivel-y. r

The curves shown in Figure 2 depict the manner in. which the outputs of tubes 2| and 22 are. modulated by two different intelligence frequencies; and combined in the load impedance .33. In Figure 2 the load currents in load resistance 33 are plotted against. time. The pulsations B were supplied by, say, tube I3 and are varied in amplitude in accordance with the modulations envelope A supplied by the audio freqeuncy transformer-l5.- P ls ions. .12 were supplied by tube l4 and..=are varied in amplitude in accordance. with the rnodulationenvelope C. supplied by the audio, fr q n y transformer Ni. A. B. and b low the zeropoint correspond to those above, and: represent-those portions of the em tted W supplied by the fly wheel efiect. of inductan e 4 and which were not present in the resistance load at 33.. I

1 The functions of tubes 2.| and 22 in Figure 1 are to combine both sets of pu sat ons ne ad impedance after they have been separatelymodulated. 'I'hese tubes are or inarily b ased by atteries 29; and 30 so tha theyfunct on as linea amplifi rs avi a nonrindu tivc a furnished by the resistance 3E3. In the plate circuit; of tu e .38 radio frequency transf mer 46-41.. onn ct d to the ant nna. s ppl es the other a of the radio frequency cycle.

The descript on.- of the operation f th t mitter iven above as illustrated y eu 2 and has. been based. upon the. a s mption th t the frequency applied to the frequencyeXci-ting transformer li -I12 is twice that applied to. the transformer I.Z-. Assuming; however, that the frequency multiplierdesignated F. D. generates a. frequency four times that of the. source which activates the transformer l-Z, it is obvious. that instead-of alternate cycles of the carrier b n modulated by the two signals, now. alternate. groups of cycles would be. diverted to. alternate. amplifier tubes and, sornodulated. each group containing two cycles, Instead of employing a frequency multiplier or frequency doubler F. D. between the sources of oscillations S. O. and the variable attenuator V. A. a, subharmonic generator may be inserted between the source of oscillations S. O. and the radio frequency amplifier R. F. A. supplying radio frequency to the phase shifter P. and thence to. the radio frequency transformer l--2.'

In the above descriptions; of the operation of the transmitter, the two-tubes l3 and have been modulated by transformers l5 and 16, in their respective plate circuits. It is conteme plated that the present. nvention includes a system in which these. tubes are modulated in theirgrid circuits also.

Alternate cycles. or groups of cycles of the carrier frequency may be diverted into means; fo separately modulating them by individual in: telligences. Part of the circuit for accomplish.-v ing this is composed in Figure 1 of adio frequency transformer l 2, tubes 3 and 4., and re-. sistances l and 8. These circuit elements or appropriate combinations. of any of them may be coupled to the plate circuits of. tubes #3 and M. instead of to their grid circuits in such manner as to divide the carrier voltage into alternate cycles or groups of cycles which. may ave been modulated ormay be subsequently modulated by separate intelligences. .Such a circuit arrangement is shown in Figure 4.

, In Figure 4 the secondaries of the modulation transformers l5. and I6 shunted by radio freouency by-passcondensers are connected to the respective control grids of tubes l3. and I4. .The other ends of the secondaries are connected together and to the cathodes of tubes [3 and 14 by way of the secondary I2 of the radio frequency transformer ll-l2? and. the source of biasing potential It. The plates of. tubes is and IA. are supplied with energizing potential from the source 28* by way of coupling. resistors 1-.23 and 8 .24 respectively. The plates of tubesl3 and [,4 are connected respectively tocoupling con densers 3| and 32 which are in turn'connected to thecontrol grids of tubes 2| and 22- respectively as shown and described in connection with Figure 1 and the grids of the tubes 21 and. 22 (Figure 4) are biased in the. same manner as the respective tubes in Figure 1. In this embodiment the outputs of tubes 3 and 4 are applied to the plate circuits of tubes l3 and I4 respectively. The plate of tube 3 is connected to that point in the plate circuit of tube l3 between the coupling resistors 1 and 23. The plate of tube 4 is connected to that pointin the plate circuit of tube I4 between the coupling resistors 8 and 24. Plate potential is supplied to the plates of tubes 3 and 4 from battery 6 connected to the filaments thereof by the connection extending from the battery 6 to the juncture between coupling resistors 1 and 8 and thence through these resistors to the respective tubes 3 and 4.

In this arrangement voltages are alternately developed across resistances 1 and 8 of such polarity that they oppose the positive voltages introduced at battery 28", and hence render tubes l3 and M, alternately inoperative by reducing their plate voltages to zero or lessinegative). As a result tubes l3 and M will alternately supply excitation to the amplifier comprising tubes 2| and 22, provided the voltages introduced in the secondary l2 of transformer ll-l2 and that existent across-resistances 1 and 8- are in the proper phaseal and magnitude relations'as before, and the operation of the circuit of Figure 4 will, as in Figure 1, provide'for the final transmitter carrier being alternately modulated by two intelligences via tubes l3 and M which are separately modulated in their grid circuits.

Figure shows an adaptation of the transmitting circuit of Figure 1 for the transmission of four intelligences simultaneously; As will be seen it comprises in part two similar-circuits, each similar to that portion of the circuit of Figure 1 included between the transformer l-2 and the pair of tubes 2| and 22 inclusive. In addition, in Figure 5 there is a push-pull'amplifier including radio frequency transformer Ell- 52, amplifier tubes 53 and 54, a source of biasing potential 55 for biasing the grids of said tubes, a source of anode potential 56 and tube load resistances 51 and 53 connected in the re spective plate circuits of tubes 53 and 54. The plate load resistances 51 and 58 are connected in series with the secondarieslZ of the transformers H'l2 in theinput circuits of tubes l3 and M of the respective upper and lower similar por tions of the circuit of Figure '7 corresponding generally to Figure 1. With the resistances 51 and 58 each connected in series with one of the secondaries 12 of one of the two duplicate radio frequency transformers I l--|Z,' plate current flow in tubes 53 and 54 via resistances 51 and 53 respectively causes a potential difference to be developed thereacross which serves to increase instantaneously the negative grid potentials of the duplicate input circuits associated with the two transformer secondaries 12. A flow of current in resistance 51 tends to produce a negative potential on the grids of tubes l3 and M in the upper portion of the diagram. A flow of current in resistance 58 tends to produce a'negative potential on the grids of the tubesflfi and M in the lower portion, of the diagram. In Figure 5 a second frequency doubleror-frequency multiplier 'F. D. is utilizedaridaf second phase shifter P; S.

is employed so that the phasal relationship of the" currents in the transformers 5l-52, l--2,

and l|l2 can be adjusted with respect to each:

other.

The operation of the circuit of Figure v5 is bestunderstood by reference to the'curve of Figure 6. Assuming first that. the radio -'frequency.

transformer 5I52 is energized .by a voltage of. frequency both radiofrequency transformersa P. 8., together with the amplifier R. F. A. -and variable attenuator VA.

In Figure 6 the individual inthe control circuits of tubes l3, L4, upperand lower sections are shown. Section A shows the individual voltages active in the input or control: circuit of upper tube l3. Section B shows-the individual voltages active in the input circuit-of upper tube I l. SectionC. shows the individual voltages active in the input circuit of lower tube, l3. Section'D. shows the individual voltages ac-' tive in the input circuit of lower tube "'l liof'Figa ure 5. In all sections (A, B, C, and D) I'ist'h'e bias supplied by batteries 9 and H). In all sections the curve II represents the voltage of fre-: quency 4 introduced at transformers l2',-and'are all in phase in all tubes. In section" A, II-Iiisthe voltage drop across the upper resistance 1;; in section B the curve III represents the voltage. drop across resistance 8; in section C the curve III is the voltage drop across'the lower resistance 1; in section D the curve III represents the voltage drop across lower resistance 8. 1 Voltage drops occur: simultaneously in both res'istances' 1. and occur simultaneously in'both resistances-'8 on the opposite half of cycle of frequencyiffrom that of resistance 1. In sections A'andB the curveIV represents the voltage drop across re;- sistance 51 occurring simultaneously in the-input circuits of upper tubes i3 and 14. 'In" section's C and D the curve IV represents the voltage-drop across resistance 58, or, in other wordsftlie -volt z age across resistance 58, which influencesthe input circuits of lower tubes l3 and lit-in phase. The voltage drops in resistances 51 and iii-occur during alternate alternations of the voltage of frequency f.

. The operation of the entire circuitof Figure!) is best explained by describingthe action at the four instants when the alternat ons of curve =II are positive. It is assumed that 'both' trans formers I2 are excited in phase and bothtr'ansforms Il-l2 are excited in phase. By referenceto-Figure 6 it is seen that at the instant of the first positive alternation of voltage in curve II; reading from left to right, voltage-I'is operative in the grid circuits of all four tubes2l'--22, v olt; age II is operative in all four grid input-circuits and corresponding tubes of both pairs'of tube's l3l4 are blocked by the negative potentialshown in curve III. In addition, tubes l'3 a'n'd M of either the lower or the upper part of the circuit of Figure 5 are further blocke'dby the negative potential shown in curve- IV developed by a potential difference existent across one o f the resistances 51 or 53. It will be assumed'for purposes of explanation that the first-voltage rise of curve III operates on both tubes l3 and the second voltage rise of curve III operates on both tubes I 4. 'Itwill also be assumed for'pu'r poses of explanation that the first negative volt agerise of curve IV operates on'the'upper' group' voltages operating" of tubes l3' and l4, and the second voltage rise of curve IV operates on the lower group of tubes l3 and M. Then the first positive alternation shown in curve II produces a plate current pulsation in the lowertube l4,-bu't in none of the others. On the second positive alternation shown in curve II, as before the voltages sh'own in curves I and II are operative in all four tube input circuits. But now the voltage corresponding to that shown in curve III blocks both tubes l4; the voltage corresponding to that shownin curve IV still blocks the upper tubes I3 and M; so that on the second-positive alternation of curve II only the'lower-tube 'l'3has a plate current pulsation. Now, on thethird positive alternation of the voltage corresponding to curve II both the lower tubes l3 and I4. are blocked by the negative voltage corresponding to curveIV,

and the upper tube l3"is blocked by the negative voltage corresponding: to curve III, so that only tube M has a plate current pulsation during the third positive alternation shown in curve II. On the fourth positivealternation of curve II both lower tubes l3 and M are still blocked by the voltage corresponding to that'of curve IV, and the upper tube I4 is blocked by the voltage corresponding to curve III, so that only the upper tube [3 has a' plate current pulsation. On the fifth positive alternation of curve II the entire cycle just described is repeated.

The output of each of the tubes l3 and=il4 is separately modulatedin itsplate circuit; and all .four: outputs are recombined in the loadiimpedance of'resistance 33.

Itis .contemplatedthat any of the modifications'of the circuitof Figure 1 may: also be applied to that of-Figure Multi-grid tubes could be used in this'arrangement in place of tubes is and I4; In asystem employing four-grid tubes, one ofwthe grids couldbe excited by the voltage supplied at transformer ll-l 2; one grid by the voltagesupplied from: resistances 7 and 8, and oneby the voltage from modulation transformers, and one by the-voltages from resistances 51 and 58. The-tubes 53-44;. 3-4, etc., couldbe enclosed in a'single'envelope having duplicate sets of elements. With this-arrangement the two grids could be separately terminated, the two platescould be separately terminated. and the two filaments orcathodes could be terminated together or be a single emitting electrode.

Referring now toFigure'l a description will be given of one form of receiving circu t for separatingathe two sets of; radio frequency cycles or groups of cycles to derive therefrom thetwo separate signals or intelligences.-. In Figure? a receivingantenna is-show nat 59 connected.v to a radio frequency amplifier, rectangle R. F. A. The output ofthe radio frequency amplifier R. FL A. is. connected to a frequency d vider', rectangle. D. The output of the frequency divider is connected tor the inputcircuit-of. a phase shifter. rectangle PCS; The outputof the phase shifter P. S. is connected totheprimaryfififof radio frequency transformer B ll- 6! Thesecondary of the transformer i;ll 6"l is center. ,tappedQ The end terminals offthe secondary BJ are connected to the control rids'ofamplifier tubes .62 and 63' respectively. The center tap of the transformer secondary 6| 'isconnectedby'means of a source of b asing potential to the cathodes or filaments of the tubes'62 and'63f The plates or anodes-of tubes 62 "anc'l63 are'conn'cted by r'espective coupling resistors "66 and -61 '-to"a "source-of plate potential $55 one terminal cr wman is connected to the cathodes or filaments of tubes 62'- and 63. The plates of tubes 62 and 63 are connected directly to the controlgrids of tubes H and 12 respectively; The cathodes or filaments of tubes H and 12' are connected together through the secondary 10 of a radio. frequency transformer 69-'!l) and a source of grid biasing potential 68 to a poin't-between the coupling resistors 66 and 61. The output of the radio frequency amplifier R. F. -A; is-also connectedto the input of a variable attenuator, rectangle V. A. The output of the variableattenuator V. A. is connected to energize the primary '69" of the transformer 69--l6f The plates-or anodes oftubes'll'and 12- are connected to respective" indicating devices 16' and" which-are preferably'audible signal indicators, for example: telephonereceivers. The other terminals of indicating devices 1 16 and "H" areconnected 'together'to: the high potential side of a source of plate potential 15gthe low potential side of which isc'onnected"to the'cathodes or filaments of tubes I I and'IZ. w By pass'condensers Hand 14 are connected'across from cathodeor filament-to anode 'or plate of 'the'respective tubes H and"; The tubes 62 and 63'are preferably normally operated as linear amplifiers biased to cut'oif by the biasing battery 64so that with no excitation from 'inductanceBl no current flow in the resistances'66 and 6l;

The two tubes "H and 12 are normally biased to cut oifbythe grid biasbattery 68in their circuits. The" resistances 66and 61 are so connected 'that any current flowing in them due to plate currents ternately flows in resistances 6G and '61.

plified by the radio frequency amplifier R. F. A.,

the output of which excites a frequency divider which in turn excites transformer 66-6l. The operation of tubes 62'63,' ll-l2 is exactly similar to the operation of the parallel group in the "transmitter Figure 1, composed of tubes 34, H

and I 'The voltage at the secondary 6| 'of transformer 6!l-6l alternately renders tubes 62 and63 conductive. Current from battery 65 al The alternate'va-riation of current in resistances 66and 6| gives rise to a voltage change therein effective to change the value of the grid potential on the grids of tubes H and 12, thus diverting alternate cycles or groups of cycles of the amplified carrier to the two detector tubes 11- and 12 where they are rectified" and delivered-"to the load circuit 16 and 11. The rate 'of alternation of the received wave in the receiver is maintained in synchronism with thatof the transmitter by using a sub-harmonicof the carrier to excite the transformer because as long as; the voltagesintroduced in.

resistances 66 and 61 have certain minimum value, the extent-of their maximum value is unimportant. Operation of'the receiver for percentages nf-modulation approaching one hundred percent of tubes 52 and-63-in Figure 7, etc.

related in all cases.

is obtained by adjusting the relative values of voltages at transformer 60S| and 69-10 so that the voltages at resistances 66 and 6! will always be sufficient toproperly counteract the maximum modulated peak voltages introduced by way of transformer 69'l0 for any given percentage of modulation,

How much further the instantaneous voltages in 66 and 6'! rise above this necessary minimum is immaterial. In certain instances where signals are modulated at high percentages, an amplitude discriminating amplifier may be inserted between the frequency divider D and the phase shifter P. 5., or the sub-harmonic frequency may be gen-'- erated' locally by a crystal oscillator which may or may not be influenced by the incoming signals;

The curve shown in Figure 8 illustrates the operation of'the receiving circuitof Figure '7. Pulsations of plate current Fiplate current plotted against time) occur in the plate circuit of tube ll, conforming to the modulation envelope E. Pulsations of plate current Hoccur in the plate circuit of tube 12 conforming to the modulation envelope G. Although both of these sets of pulsations are positive, they are drawn in different directions from the zero axis to indicate that they are supplied by different tubes. The current which produces the signal-in indicating devices 1.6 and 11 respectively is the average value of the plate current pulsations occurring'at radio frequency in the tubes H and 12. As a result of diverting alternate cycles or groups of cycles of the carrier to different detector tubes; the average valueof the plate current in each tube is reduced by one-half, but the shape of a modulationenvelope remains the same. i

It will be apparent that the'circuit arrangement of Figure 4 may also beused as anadaptation of the receiving circuit of Figure'l.

The receiving circuit of Figure? maybe adapted to receive four signals simultaneously transmitted from a transmitter similar to that shown in Figure when the receiving circuit of Figure 7 is modified in accordance with the teachings of Figure '7, the modification ofwhich appears to be obvious. In this case two frequencies would have to be derived from the received carrier, being onehalf and one fourth of the carrier frequency.

t is understood that while in the drawings batteries have been shown as a'source of supply of grid and plate voltages-for all tubes, any other suitable source could be used. It is also understood that separate sources of. potential may-be employed where common sources have been shown and vice-versa, provided no undesirable coupling between the circuits is introduced thereb 1 Many other modifications of the above circuits are possible, and the drawings referred to are only representative and are not intended to limit'the invention thereby, nor are the descriptions to be. considered as limitations.

shifter P. S. might be'eliminated under certain circuit conditions. Diode rectifiers could be used in place of tubes '3 and 4 in Figure 1 and in place The frequencies ,f, 2f, vetc'., need ,not be harmonically embodiments of my invention are not to be restricted by the foregoing specifications or by the accompanying drawings, butonly by the scope of the appended claims.

The above described invention may be used by or for the Government of the United States with- V out the payment of any royalty thereon.

Itis understood that the What I claim is:

l. A system for receiving and separately detecting a plurality of signals impressed upon a carrier in alternate order comprising means for intercepting and amplifying said signals, means for deriving fromsaid amplified signals oscillations having a sub-harmonic relation to'the carrier, a pair of thermionic tubes having at least a cathode, a control electrode, and an anode, means for applying to the control electrodes of said tubes-a direct current component of potential of such value that substantially no anode current flows therein in the absence of the application of other components of potential to the control electrodes of said tubes, means for applying at least a portion of the received amplfied signals to the control electrodes of said thermionic tubes in phase, means for impressing upon the control electrodes of said tubes additional components of potential of said sub-harmonic frequency in phase opposition in the two tubes and signal indicating'devices operatively associated with the output circuits of each of said tubes.

2. A system for receiving and separately detecting a plurality of signals impressed upon a carrier in alternate ordercomprising means for intercepting and amplifying said signals, means for deriving from said amplified signals oscillations having a sub-harmonic relation to the carrier, a pair of thermionic tubes having at least a cathode, a, control electrode, and an anode, means for applying to the control electrodes of said tubes a direct current component of potential of such value that substantially no anode current flows therein in the absence of the application of other components of potential to the control electrodes of said tubes, means for applying at least a portion of the received amplified signals to the control electrodes of said thermionic tubes in phase, means for alternately impressing upon the control electrodes of said tubes an additional component of potential of said sub-harmonic frequency whereby anode current flows alternately in the output circuits of said tubes, and signal indicating devices operatively associated with the output circuits of each of said tubes.

3. A radio receiving system for receiving and separately detecting transmitted signals of frequency 2f transmitted from a system in which alternate intelligences modulate a single carrier comprising means for receiving and amplifying said signals, means for deriving from said amplified signals oscillations having a frequency f, a pair of thermionic tubes having at least a cathode, a control electrode, and an anode, means for applying to the control electrodes of said tubes, a direct current component of potential of such value that substantially no anode current flows therein in the absence of the application of other components of potential to the control electrodes of said tubes, means for applying at least a portion of the received amplified signals of frequency 2f to the control electrodes of said tubes in phase, means forimpressing upon the control electrodes of said tubes alternately at the frequency J, an additional potential to prevent anode current flow in each of said tubes alter nately, and signal indicating devices connected least two thermionic vacuum tubes each having at least a cathode, a control electrode, and an anode, means for applying to the control electrodes of said tubes a direct current component.

of potential of such value that substantially no anode current flows therein in the absence of,

the application of other components of potential to the control electrodes of said tubes, means for applying to the control electrodes of said tubes potentials corresponding to said signals in phase in said tubes, means for increasing the biasing potential applied to the control electrodes of said tubes alternately at said sub-harmonic frequency, and signal indicating means connected in the anode circuits of each of said tubes.

5. A radio receiving system for receiving and separately detecting transmitted signals of frequency 2nf transmitted from a system providing means for modulating the carrier alternately with different intelligences comprising means for deriving from said received signals oscillations having a frequency wherein n is any integer, a pair of thermionic tube detectors having at least a cathode, a control electrode, and an anode, means for applying to the control electrodes of said tubes a direct current component of potential of such. value that substantially no anode current flows therein in the absence of the application of other component of potential to the control electrodes of said tubes, means for applying at least a portion of the signals of frequency 2n to the control electrodes of said thermionic tube detectors in phase, means for impressing upon the control electrodes of said detector tubes in phase opposition other potentials of frequency f derived from said signals, the phase and amplitude of the two potentials so impressed upon the control electrodes of said detectors being of such order that anode current may flow in said detectors alternately, and signal indicating devices operatively associated with each of said detectors.

6. A receiving system for dividing a modulated carrier modulated alternately with two different intelligences, and separately detecting and indicat ng said intelligences comprising in combination at least one pair of thermionic detector tubes each having at least a cathode, a control grid and an anode, means for applying a direct current component of biasing potential to the control grids of said tubes of such value that substantially no anode current flows therein in the absence of the application of other components of potential to the control grids of said tubes, means for exciting the control grids of said tubes in phase by said modulated carrier, means for de riving an alternating current potential sub-har-- monically related to said carrier frequency, means for separately rectifying both half-waves of said potential, means for applying the rectified half-' wave components of potential to the grids of re-- spective ones of said tubes so as to add to thedirect current component of biasing potentialapplied thereto whereby the tubes of said pair are rendered inoperative as detectors in alter nate order, and signal indicating devices con-' nected with each of said detector tubes.

7. A receiving system for dividing and detecting a modulated carrier modulated cyclically with four different intelligences comprising in combination at least two pairs of thermionic detector tubes each. having at least a cathode, a control grid and an anode, means for applying a direct current component of biasing potential to the control grids of said tubes of such value that substant ally no anode current flows therein in the absence of the application of other components of potential to the control grids of said tubes, means for exciting the control grids of said tubes inv phase by said modulated carrier, means for deriving an alternating current potential of half the frequency of said carrier, means for separately rectifying both half-waves of said current, means for applying the rectified halfwave components of potential to the grids of respective pairs of said tubes so as to add to the direct current component of biasing potential applied thereto, means for deriving an alternating current potential of one-fourth the frequency of said carrier, means for separately rect fying both half-waves of said current, means for applying the rectified half-wave components of potential to the grids of respective pairs of said tubes so as to add to the direct current components of biasing potential applied thereto whereby one after another of said tubes is rendered operative to pass anode current while the other three of said tubes are rendered inoperative, and signal indicating devices connected with each of said tubes.

MAURY I. HULL. 

